1. Field of the Invention
The present invention relates to a seat suspension device for an automotive seat, and in particular relates to an improvement of a seat suspension device which uses a biasing means such as a torsion bar or other elastic element for adjustment of seating height elastically according to the weight of a an occupant on the seat.
2. Description of the Prior Art
In most of ordinary seat suspension devices, there has been employed a spring or torsion bar as a biasing means in order that the seat frame on the suspension device is kept biased upwardly to elastically support an occupant on the seat.
Let us assume that the torsion bar is used in the seat suspension device, the conventional types thereof are, by and large, of the construction that an operation lever is rotatably secured on one side of a seat frame and coaxially connected with a cam having plural discrete cam surfaces, and a torsion bar is interposed between the upper seat frame (i.e. seat cushion frame) and lower base frame fixed to a floor of automobile, with one end of the torsion bar being abutted against one of the discrete cam surfaces of the cam. The rotation of the operation lever causes the simultaneous rotation of the cam, so that another different cam surface is contacted with the one end of the torsion bar, thus resulting in the change of the torsion stress of the torsion bar to bring about the adjustment of upwardly biasing force upon the seat. An occupant therefore may attain an optimal seating height according to his or her weight.
In such prior art, a locking means is provided independently of the suspension device, to permit locking and unlocking of the upper seat frame against the lower base frame. An example of this locking means is found from the U.S. Pat. No. 4,566,667 in which the locking mechanism is disposed forwardly of the seat frame, comprising an operation lever, a lock plate having a series of hook-like engagement notches, and a lock pin. When the operation lever is rotated, the lock plate is rotated simultaneously to bring one of the notches into engagement with or disengagement from the lock pin for locking/unlocking purposes, allowing the adjustment of seating height.
However, the above-mentioned prior art is disadvantageous in that an occupant on the seat has to experience quite annoying trouble of standing away from the seat and bending his or her body to reach the operation lever for unlocking and locking operations in order to adjust the seat suspension device, and further in that the operation procedures involves two separate steps of: first, rotating the lever of the locking mechanism to unlock the seat suspension device, and second rotating the lever associated with the cam for adjustment of the biasing means. Hence, the operationability of the prior art is poor, requiring much labor effort on the part of the occupant, and thus being time-consuming.